NEA Monthly News Bulletin, January 2010

Recently issued CSNI reports

 

CSNI/R(2009)5 – State-of-the Art Report on Nuclear Aerosols. This new reprot on nuclear aerosols provides updated information on aerosols needed to address source term in severe accident conditions. Following the introduction, Chapter 2 discusses the fundamentals of aerosol behaviour with a bibliography of the pertinent literature. Chapter 3 is devoted to the topics of aerosol formation/growth, transport, and retention and release. Chapter 4 provides descriptions of codes for modelling circuit and containment aerosol behaviour, and Chapter 5 describes the experiments used for their validation. Chapters 6 and 7 provide examples of validation results and plant applications of source term calculations. Chapter 8 summarises the findings of the 1998 Cologne Workshop and progress made since, and provides recommendations for future work.
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CSNI/R(2009)9 – Proceedings of the Workshop on Ageing Management of Thick-walled Concrete Structures, Including In-service Inspection (ISI), Maintenance and Repair, Instrumentation Methods and Safety Assessment in View of Long-term Operation held in Prague, Czech Republic, on 1-3 October 2008. State-of-the-art techniques for the integrity assessment of concrete structures were discussed at this workshop to recommend areas in which further research is needed. Special emphasis was given to performance-based ISI based on non-destructive examination (NDE) methods (such as impact echo, ultrasound and high frequency radar) and instrumentation. Limits of applicability were extensively discussed. The management of ageing programmes based on suitable structural monitoring was also addressed in the framework of a safety assessment of the installations in the long term. Probabilistic methods oriented towards reliability structural assessment were also discussed for consistent management of the integrity assessment of civil structures, both repairable and not.
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CSNI/R(2009)11 - Proceedings of the Workshop on Justifying the Suitability of Nuclear Licensee Organisational Structure, Resources and Competencies - Methods, Approaches and Good Practices held in Uppsala, Sweden on 8-10 September 2008. Among important attributes identified that characterise a “good” organisation were openness to learning from experiences, systems perspective in plant management, safety-oriented decision making and need for clear lines of responsibility and accountability. The workshop distilled a number of key messages on the assessment process, the licensee actions and the regulatory actions.
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CSNI/R(2009)12 - Proceedings of the Workshop on Experiments and Computational Fluid Dynamics (CFD) Code Application to Nuclear Reactor Safety (XCFD4NRS) held in Grenoble, France on 10-12 September 2008. These proceedings contain five keynote lectures, summaries of the activities of three CFD writing groups of the Working Group on Analysis and Management of Accidents (GAMA), and 59 technical papers presented in the following sessions: Horizontal flow - Pipe flow  (HOR), Accident analysis (AC), Pressurised thermal shock - Direct contact condensation (PTS), Mixing issues (MIX), Boiling flow, bubbly flow and critical heat flux (BOI), Multi-scale analysis (MS), Containment thermal-hydraulics (CO), Core and steam generators (CSG) and Advanced reactors (AR). The proceedings also contain session summaries prepared by the session chairs.
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CSNI/R(2009)13 – BEMUSE Phase V Report - Uncertainty and Sensitivity Analysis of a Large Break, Loss-of-Coolant Accident (LB-LOCA) in the Zion Nuclear Power Plant. Sensitivity analysis has been successfully performed by all participants using the probabilistic method. A comparison has been carried out on influence ranking of the uncertain parameters and the following ones were found influential: “Power after scram” and “UO2 conductivity” for the cladding temperature, “Containment pressure”, “Initial intact loop cold leg temperature” and “Initial upper head temperature” for the primary pressure, “Film boiling” and “Critical heat flux”. The report also contains a comparison with Phase III, although final conclusions will be provided in the Phase VI report.
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CSNI/R(2009)14 – Proceedings of the Workshop on Taking Account of Feedback on Sump Clogging held in Paris on 4-5 December 2008. The objective was to exchange information about steps made so far to address the sump clogging safety issue, since its identification with the 1992 event at Barsebäck, and its resolution. Actions taken or planned to be taken by regulators were presented in a first session. A second session exchanged information on industrial solutions and their safety assessment for both operating and future reactors, and in the last session views on unresolved issues and future developments were discussed.
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CSNI/R(2009)16 – Probabilistic Risk Criteria and Safety Goals. This report provided results of a survey on the use of probabilistic risk criteria in 13 countries. Probabilistic safety criteria, including safety goals, have been progressively introduced by regulatory bodies and utilities. They range from high-level qualitative statements (e.g., “The use of nuclear energy must be safe”) to technical criteria (e.g., probability of fuel cladding temperature being higher than 1204°C).They have been published in different ways, from legal documents to internal guides. They can be applied as legal limits (not meeting them being an offence) or merely “orientation values”.
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CSNI/R(2009)17 – Low Power and Shutdown Operations Risk. This report presents the development of a structure for the creation of an information base and assessment of modelling issues about low power and shutdown (LPSD) operations risk. It also addresses insights from recent LPSD investigations and operating experience, and shares information on analysed initiating events and applied methods. Finally it attempts to collect and share information on how inadvertent human actions resulting in initiating events (IEs) are taken into consideration in LPSD operations' probabilistic safety assessments (PSAs).
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CSNI/R(2009)18 – Recommendations on Assessing Digital System Reliability in Probabilistic Risk Assessment of Nuclear Power Plants (NPPs). This report makes recommendations regarding current methods and information sources used for quantitative evaluation of the reliability of digital I&C (DIC) systems for PSAs of NPPs, and identifies, where appropriate, the near- and long-term developments that would be needed to improve modelling and evaluating the reliability of these systems. The recommendations are grouped into the following three categories: method development, data collection and analysis, and international co-operation.
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